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Factories and traffic blamed for 'the hum'

Not all the people plagued by a mysterious low frequency hum are imagining
it. At least 20 per cent of sufferers tested were hearing a real noise,
says British Gas, which has been investigating the problem.

Following complaints made to Ofgas, the gas industry watchdog, by the
Low Frequency Noise Sufferers Association, British Gas has conducted the
most extensive scientific analysis of the hum yet. The association suspected
that gas pipeline pumps were to blame.

British Gas studied 33 complaints, continuously monitoring sound in
the sufferers’ homes with very sensitive analysers. British Gas believes
the generic cause of the problem is high-frequency attenuation. When sound
from roads, factories, offices or natural air currents travels over a long
distance, the high frequencies soon fall off but the lower frequencies carry
on. Rooms of a certain size and shape amplify the sounds, and the effect
varies with the weather. People whose ears are sensitive to low frequencies
then hear noises which they cannot recognise.

British Gas is convinced that the turbines it uses to pump gas through
transmission pipelines are not the main culprits. The pumps work only a
fraction of the time and so cannot be responsible for complaints about continuous
noise.

Of the 33 cases, British Gas found one where the noise was caused by
resonance in its gas pipework. Others were traced to a refrigerator at a
meat packing plant, a power unit on a ship 5 kilometres away, an industrial
burner, a distant shipyard, machinery in a knitting factory and a resonating
flue.